Focusing mount

ABSTRACT

A focusing mount includes a focusing frame fixed to a focus tube with at least one lens having an optical axis which is connected to a constraining frame by prismatic joints for enabling movement of the focusing mount along the optical axis without any twisting, lateral, rotational or swing movements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved lens mounting system whichprovides all the benefits of a simple sliding tube but without theassociated drawbacks, and more particularly to a focusing mechanismwhich moves a focusing frame along the optical axis of each lens systemlinearly by constraining lateral, rotational and swing movements.

2. Description of the Prior Art

There are many ways to focus a lens. This invention concerns thefocusing of a lens by means of mechanically changing its position alonga fixed path, which maintains the orientation of the lens and followsthe optical axis of the lens. This movement may be achieved by manualoperation, or it can be motorized. This invention does not cover methodswhich involve using electronic or other means to change the shape oroptical properties of a lens to achieve change in focus.

In an imaging device, when a lens is moved along its central opticalaxis, it is desirable for it not to shift or tilt with respect to thisaxis. This is because an imaging device requires an image capturing filmor sensor to be placed in a fixed position at a predetermined focalplane. If the lens tilts or shifts, its optical axis and focal planewill tilt or shift with it. For conventional devices, it is notpractical to move the image capturing sensor in concert with any tilt orshift of the lens. Any uncontrolled shifting or tilting will degrade thequality of the focus. Even a small tilt in the orientation of the lenswill result in an image becoming blurred even when the lens has beenmoved to its correct point of focus on the optical axis. This means thatthe lens will effectively have to move along one optical axis which endswith the predetermined position of the image capturing sensor on thefocal plane.

It is also desirable for the movement of the lens to be achieved withmaximum efficiency to facilitate ease of use and economy of space. Thisis especially important where there is motorization or automation of thefocusing mechanism.

Many systems have evolved to move a lens along its optical axis withoutshifting or tilting. This invention concerns systems which consist of afixed constraining frame and a moving focusing frame on which the lensis mounted. The focusing frame, constrained by the constraining frame,guides the lens along its optical axis.

FIG. 1A depicts a concentric sliding tube lens focusing systemconsisting of a rigid outer focusing tube and a rigid inner focusingtube. An outer focusing tube 01 serves as a rigid housing to which afixed constraining frame 02 is attached. An inner focusing tube servesas a moving focusing frame 03. A lens 04 is mounted in the focusingframe 03. The focusing frame 03 slides in and out of the constrainingframe 02. Movement in all other axes other than the optical axis areconstrained. The lens 04 cannot shift or tilt on its optical axis. Itdoes however rotate. This movement of the lens relative to the focalplane 05 achieves the desired lens focusing function of the system. Animage capturing device such as a CCD or film can be situated on thefocal plane 05. A simple example of such a focusing device can be foundin a basic pirate's telescope.

In practice, if there is full contact between the outer cylindricalsurface of the focusing frame 03 and the inner cylindrical surface ofthe constraining frame 02, a large amount of friction will be introducedinto the system.

For this reason, such systems are built with contact points at the twoends to support the inner focusing tube and locate the optical axis. Therest of the facing surfaces do not need to be in contact. Thiseliminates the possibility of the inner focusing tube being supportedinadvertently at some point between the two end points, therebyshortening the length of the constraining frame. It also reducesfriction and allows one tube to slide freely inside the other. The outersupport tube functions as a constraining frame, because only the twocontact points at either end are used for supporting the inner tube. Thetube is merely a convenient shape for the device. It is unnecessary anddifficult to manufacture rigid concentric tubes of sufficient precisionto slide in and out of each other with full contact.

The key to a smoothly working concentric tube focusing system is theratio of the diameter of the constraining joint as defined by thefocusing frame to the length of the constraining frame. It is the twopoints of support at the extreme ends of the constraining frame which dothe work of keeping the inner focusing frame in place while it is beingmoved.

FIG. 1B depicts a modified version of the focusing system in FIG. 1Awith a constraining frame 10, focusing frame 11 and lens 04. It is goodpractice to design the tubes so that the ratio in length (A) of theconstraining frame 10 to the diameter (B) of a constraining joint 07 isapproximately 7 to 1 or greater. Otherwise, the focusing frame 11carrying the lens 04 can rock within the constraining frame 10. Theresult would be that the lens 04 can deviate from its ideal position onthe optical axis. 12.

In fact, depending on the size of the gap between the concentric tubesfunctioning as a focusing frame 11 within a constraining frame 10, ifthe ratio of A/B approaches 1, which would be a short constraining framelength for a given constraining joint diameter, the focusing frame 11can tilt so much within its constraining frame 10 that it will jam andnot slide at all.

In theory, one can design a lens tube with a small constraining joint, along constraining frame and long focusing frame, and this will be a verystable and accurate focusing system. In practice, the focusing system inFIG. 1B needs to function as part of an overall imaging device. Theconstraining frame and focusing frame need to accommodate peripheral aswell as principal light paths entering the imaging device, passingthrough the lens, and falling on the focal plane. The longer the frames,the narrower the angle of view.

The designer of the overall imaging device will desire as much room aspossible on either side of the lens, and as much flexibility in theangle of view as possible. This can only be achieved by making theconstraining frame and focusing frame as short as possible in order toreduce the thickness of the imaging device. This inevitably leads to theproblems with a concentric tube system jamming when the ratio of thelength (A) of the constraining frame 10 and the diameter (B) of theconstraining joint 07 is insufficient.

Another implementation of the fixed constraining frame and movingfocusing frame method is depicted in FIG. 1C. A constraining frame 14with a helical thread and a focusing frame 13 with a matching helicalthread are combined to form a strong but movable constraining joint.This constraining joint is strong, and prevents tilt and shift of thelens because it provides axial support with each thread surface. Theratio of constraining frame 14 to the constraining joint can thereforebe reduced. Focusing systems using a helical method can have a shortouter constraining frame 14 and large inner focusing frame 13 (largeconstraining diameter). Such a system prevents tilt and shift, but thelens 04 and focusing frame 13 will rotate within the constraining frame14.

One variation of the helical thread system uses a double helical threadand two anti-rotation pins to move the lens plane in and out without thelens rotating at the same time.

In the system using concentric tubes and helical threads, the lens 04and the focusing frame 13 are situated inside the constraining frame 14.This is a limitation inherent to the system.

Any helical thread, by nature, introduces drag and inefficiency. This isbecause the outer moving surface must move a long distance in order forthe lens to move a short distance. Also, the total contact area is muchgreater than for a concentric tube system, where the focusing frame isonly supported at two ends.

A focusing system involving helical threads is inherently more difficultand expensive to make than one using concentric tubes. It requiresaccurately cutting two mating and interchangeable helical threads. Thisis not easy to mass-produce. Mass-production in plastic of such highprecision male/female helical thread tubes would require highlyexpensive precision molding equipment.

An auto focus lens with helical thread requires a high precision fit inwhich there is no slack and the fit is not too tight. This helps reducethe power required to drive the focusing mechanism and extends batterylife. This balance is very difficult to attain in production.

FIG. 2A is a side view of a slider-and-track based focusing system. Afixed constraining frame 15 is in the form of a pair of tracks whichsupport and constrain a focusing frame 16, which is attached to andguides a lens tube 17, in which is mounted lens 04. The lens tube 17 hasa clearance fit in the rigid outer focusing tube 01. The constrainingframe 15 is fixed to the outer focusing tube 01, but is no longerconcentric with it or the lens tube 17.

An axis 18 of the focusing frame 16 is parallel to the optical axis 12.The tracks which act as the constraining frame may be cylindrical asshown in FIG. 2A, but may also be in some other shape. There are alsotrack-based focusing systems which only use a single track. The focusingframe 16 can be moved along the constraining frame 15 using variousmethods, such as a rack and pinion system.

The position of the constraining frame 15 in FIGS. 2A, 2B serves toseparate the constraining and focusing frame mechanism from the lens 04.The lens no longer needs to be situated in a pair of concentric tubes,which in turn would have their diameter determined by the size of thelens. This means that within the limits imposed by materials andworkmanship, it is possible to design a sliding track with a very smalldiameter (A) of the constraining joint as defined by the focusing frame16 and a length (B) of the constraining frame 15 similar to the length Bof the constraining frame 08 in FIG. 1A.

In a track-mount based focusing system, there is no rotation of thelens. Tilt and shift are prevented by means of the constraining framebeing made of very strong material, and the constraining frame andconstraining joint being very precisely engineered to have no slack onthe constraining joint while still allowing the smooth movement. Thisbalance is very difficult to attain in production. It would also requirethe use of materials much stronger than plastic.

SUMMARY OF THE INVENTION

An object of the invention is to provide a focusing system for lenseswherein a focusing frame is moved relative to a constraining frame whichmaintains the movement of the lens or lenses along their optical axiswithout subjecting the lens to any lateral, rotational or swingmovement.

Another object of the present invention is to provide a focusing systemfor lenses where a focusing frame is moved relative to a constrainingframe using only linear movements and no twisting motion.

Still a further object of the present invention is to provide a focusingsystem incorporating a focusing frame slotted with a constraining framewith two pairs of sliding joints.

Yet an additional object is to incorporate the foregoing objects in athree-dimensional focusing system.

A still additional object is to effect the foregoing objects in aneffective and efficient manner.

The foregoing objects are achieved by means of a focusing frame fixed toa lens-holding focusing tube, and movably connected to a constrainingframe. The focusing frame is connected to the constraining frame byprismatic joints (in the preferred embodiments, pin and hole joints andpin and open-slat joints are described) which constitute purely linearmotion along the respective joint axis. The joints used in the preferredembodiments of the invention incur very low frictional force. There isno shifting, tilting or rotation (pitching or yawing) of the focusingframe as it moves relative to the constraining frame, so movement of thefocusing frame is always along the optical axis of the lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional schematic side view of a concentric slidingfocusing system according to the prior art.

FIG. 1B is a variation of the view shown in FIG. 1A according to theprior art.

FIG. 1C is a cross-sectional schematic side view of a fixed constrainingframe and a moving focusing frame being joined by matching helicalthreads according to the prior art.

FIGS. 2A and 2B are cross-sectional schematic side and front sectionalviews of a slider-and-track based focusing system according to the priorart.

FIGS. 3A, 3B and 3C are respectively front, top cross-sectional and sidecross-sectional schematic views of an embodiment of the invention.

FIGS. 3D and 3E are respectively front and side cross-sectionalschematic views of a variation of the embodiment shown in FIGS. 3A-3C.

FIGS. 4A-4C are respectively front, side cross-sectional and topschematic views of another embodiment of the invention.

FIGS. 5A-5D are respectively top and side perspective, front, top andother side perspective and bottom side perspective schematic views ofanother embodiment of the invention.

FIGS. 6A-6D are respectively top and side perspective, front, top andother side perspective and bottom side perspective schematic views ofanother embodiment of the invention.

FIG. 7 is a top and side perspective schematic view of a variation ofthe embodiment shown in FIGS. 6A-6D.

FIGS. 8A-8D are respectively top and side perspective, top, topcross-sectional and another top cross-sectional views of anotherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 3A, 3B and 3C depict the invention in its most basic form.

In the concentric tube method, the outer tube is the constraining frame.It is fixed to the housing, and thereby provides support and rigidity tothe focusing frame, which holds and constrains the motion of the lensalong the required optical axis.

In FIGS. 3A, 3B and 3C, a constraining frame 19 is still part of a fixedhousing. In fact, the entire housing functions as the constrainingframe. This provides support and rigidity and constrains the motion ofthe lens 04 along the optical axis 12. However, this constraining frame19 no longer supports and guides a long, thin inner focusing frame.Instead, the focusing frame is only represented by means of fourfocusing rails 20. (As used herein, the term “focusing rail” mans a partfixed to the focusing frame, and the term “constraining rail” means apart fixed to the constraining frame.) Each focusing rail 20 has twofreely sliding hole and pin joints 21. This means there are a total offour hole and pin joints 21 at each end of the constraining frame 19.The four hole and pin joints 21 at the far end from the lens 04 areformed by the end pieces of the focusing rails and bush pieces joined tothe constraining frame 19. The other four hole and pin joints 21 areformed from pins joined to the inside wall of a focusing frame 23 andholes in the walls of the constraining frame 19. These four pairs ofhole and pin joints 21 are constraining joints joining the focusingframe 23 to the constraining frame 19. Each hole and pin joint 21 allowsthe focusing rail to slide along an axis passing through the center ofthe hole, but rotation is prevented by the presence of the otherfocusing rails joined to the constraining frame 19 by the other pin andhole joints 21.

The lens tube 17, fixed to the focusing frame 23 consisting of fourfocusing rails 20, holding the lens 04 moves in and out of an opening inthe fixed constraining frame 19, but the moving focusing frame,consisting of four focusing rails 20, wraps around the constrainingframe 19 on the outside. The four focusing rails 20 are joined at theend close to the lens tube 17 to form a rigid focusing frame, whichslides freely on the four pairs of free-moving pin and hole joints 21,guiding the lens 04 very accurately along the optical axis 12.

As described earlier, this provides sufficient support and accuracy formotion of the focusing frame relative to the constraining frame withoutengaging the entire surface area, which would unnecessarily increasefriction in the device. It functions like a focusing rail 20, butderives its strength and freedom of movement from multiple joints withthe constraining frame 19. Due to the long moment arm between the pairsof constraining joints, the reaction forces at the joints arecorrespondingly light. The frictional force becomes minute.

In FIGS. 3A-3C, the internal diameter of the constraining frame 19 isnow represented by diameter (B), which is a fraction of thecorresponding diameter (B) of the constraining frame 10 in FIG. 1B. Thelength of the constraining frame 19 is represented by length (A). Thediameter (B) of constraining frame 19 can be very small and is onlyrestricted by the need for rigidity of a pin sliding in its mating hole.By careful design, the length (A) of constraining frame 19 can bemaximized by placing the contact joints between the constraining frame19 and the focusing frame 23 made up of four focusing rails 20 at theextremes of the constraining frame 19 such that they move along axeswhich are parallel to the optical axis 12. This can be achieved withoutadding substantially to the overall length of the constraining frame 19.

As explained previously, a large ratio of the length (A) of theconstraining frame to diameter (B) of the constraining frame gives riseto a focusing frame which does not tilt within its constraining frameand does not rock when sliding with respect to the support frame.

FIGS. 3D-3E depict another embodiment of the system using a constrainingframe and four focusing rails. As described previously, the fourfocusing rails 20 in FIGS. 3A-3C are joined at the end close to the lens04 to form a rigid focusing frame 23 which holds the lens tube 17 andlens 04.

The functionality and strength of the mechanism depicted in FIGS. 3A-3Ccan also be achieved in FIGS. 3D-3E by inverting the hole and pin joints21 on the side close to the lens 04 such that the pins are joined to theconstraining frame 19 and the holes are in the wall of the adjoining armof the focusing frame 23.

The focal plane 05 can also be moved outside the housing, to the otherside of the lens 04.

In FIGS. 4A-4C, two of the four focusing rails forming the focusingframe 23 have been taken away, leaving two at opposite sides of theconstraining frame 19. This structure retains the long moment armbetween pairs of constraining joints necessary to have a smooth travel.However, without the bracing pair of focusing rails at 90 degrees, itcan pitch, or rotate about the Z-axis while it is moving. A rigidU-piece or constraining frame rails 28 is fitted to wrap around theconstraining frame 19 and is pinned to the focusing frame 23, which itintersects on the top and bottom sides, by means of two slot and pinjoints 31, which only permit limited sliding movement along the Z-axis.A frame around the constraining frame 19 is completed when the two armsof the U-piece 28 are linked up with a shaft 24 and pivoted on tworotating hole and pin joints 29 formed in conjunction with bush piecesin the wall of the constraining frame 19. The U-piece 28 is thereforelinked to both the focusing frame 23 and the constraining frame 19.

The two slot and pin joints 31 prevent the focusing rails 20 making upthe focusing frame 23 from pitching (rotating on the Z-axis) while it ismoving. In FIG. 4C, the sliding hole and pin joints 21, 22 at either endof the focusing rails 20 making up the focusing frame 23 prevent thefocusing frame from yawing (rotating on the Y-axis while it is moving).

In FIG. 5A, the rigid U-piece 28 in FIGS. 4A-4C has been split and isnow represented by an upper right adjoining piece 32 joined to the upperend of a shaft 33 by a fixed upper left hole and pin joint 34 and alower right joining piece 35 joined to the lower end of the same shaft33 by a fixed lower left hole and pin joint 36. The shaft 33 on theright-hand side passes through two bush pieces 37 on the right-hand sideof the constraining frame 19, which allows the combination U-piece onthe right-hand side to freely pivot as if locked in a pin and holejoint. The upper right adjoining piece 32 is shaped like the letter “L,”providing a long lever which can be used for pivoting the U-piece,comprised of the upper right adjoining piece 32, lower right adjoiningpiece 35 and shaft 33, in the bush pieces 37.

The rest of the U-piece is now represented by two identical levers, anupper lever 39 resting on the upper face of the constraining frame 19and a lower lever 40 resting on the lower face. The right-hand side ofthe upper lever 39 is joined to the left-hand side of the upper rightadjoining piece 323 by an upper pin and open slot joint 41. Theright-hand side of the lower lever 40 is joined to the left-hand side ofthe lower right adjoining piece 35 by a lower pin and open slot joint42.

The left-hand side of the upper lever 39 has a hole 43. The left-handside of the lower lever 40 also has a hole 44. There are two bush pieces45 on the left side of the constraining frame. The upper lever 39 islinked to the lower lever 40 by a shaft 46 on the left-hand side thatpasses through the holes 43 and 44 aforementioned and the two bushpieces 45. Depending on the application, the link between the shaft 46on the left-hand side and the upper and lower levers 39 and item 40 caneither be fixed for free floating.

In a working device such as an imaging device with a focusing lens, thefar end of the upper right adjoining piece 32, which is shaped like alever, has an index mark 47, which would point to a graduated focusingscale 48 as it is moved. This would allow the user to control the focusof the device. The focusing scale 48 will work well as long as the focusmarkings are synchronized to the actual focal point 06 of the imageforming lens 04. In real world mass-production, there is usually a rangeof focus points in any given sample of focusing lenses. Even a smalldiscrepancy in the focus point 06 can lead to a misalignment of theindex mark 47 on the lever with the focusing scale 48. To correct thisproblem, another embodiment of this invention provides an assembly-timemethod for trimming the focal point 06 of the focusing lens 04 tocorrect the focus discrepancy. To function properly, this focus trimmingmethod must work independently of the main focusing lever, which isrepresented by the upper right adjoining piece 32.

The upper lever in FIGS. 5A-5C is transformed in FIGS. 6A-6D into ashort upper-left adjoining piece 50 and an upper differential piece 51in the middle, which are joined by a rotating hole and pin joint 52. Thelower lever 40 in FIGS. 5A-5C is transformed in FIGS. 6A-6D into amatching short lower-left adjoining piece 53 and lower differentialpiece 54 which are joined by another hole and pin joint 55.

In FIGS. 6A-6D, the short upper-left adjoining piece 50 is joined to ashaft 46 by a fixed upper hole and pin joint 43. The shaft 46 is passedthrough two bush pieces 45 joined to the constraining frame 19, in whichit can freely rotate. The other end of the shaft is then joined to theshort lower-left adjoining piece 53 by the fixed lower hole and pinjoint 44. The combination of the left upper and left lower adjoiningpieces 50, 53 and the shaft 46 on the left side becomes a truncatedU-piece, which is rigid, but pivots within the constraining bush pieces45.

The two truncated U-pieces described in FIGS. 5A-5D and FIGS. 6A-6Dabove, with a pair of upper and lower differentials 51, 54 in between,which prevent pitching of the focusing frame 23, provide two independentmechanisms for adjusting the focal point 06 of the lens 04. Onemechanism, controlled by the focus lever, is used by the user to focusthe lens according to the focus markings. The other mechanism,controlled by the position of the pair of differentials 51, 54, is usedto trim the focal point of the lens 04 so that it matches the positionof the focusing scale 48.

In FIGS. 6A-6D, the movement of the U-piece on the right, consisting ofthe upper right adjoining piece 32, shaft 33 on the right-hand side, andlower-right adjoining piece 35, causes the upper and lower differentialpieces 51, 54 to move in sympathy, which in turn moves the focusingframe 23 along the optical axis 12. Movement of the U-piece on the left,comprised of the upper left adjoining piece 50, left-hand shaft 46 andlower-left adjoining piece 53, also causes the upper and lowerdifferential pieces 51, 54 to move in sympathy, which in turn also movesthe focusing frame 23 along the optical axis 12.

For any given position of the focusing lever embodied by the upper-rightadjoining piece 32, as determined by the focusing scale 48, the focalpoint 06 of the focusing lens 04 can be checked and trimmed by changingthe position of the left-hand side U-piece. When the focusing lever isset to a given position, the upper and lower pin and open slot joints41, 42 become two pivot points about which the pair of upper and lowermid-section differential pieces 51, 54 can pivot. Once the optimalposition has been found, the left-hand side U-piece can be locked down,and the focus trim of the lens unit fixed to coincide with the presetfocusing scale 48, as shown in FIG. 7.

In another embodiment of the invention, the freely rotating truncatedU-piece on the left is made adjustable and lockable. As shown in FIG. 7,the upper left adjoining piece 50 in FIGS. 6A-6D is transformed into aquadrant-shaped adjustment piece 57. The quadrant-shaped adjustmentpiece 57 is provided with a screw-and-track locking mechanism 58 inbetween the upper left hole and pin joint 43 and the rotating hole andpin joint 52 joining the quadrant-shaped adjustment piece 57 to theupper differential piece 51. The potential arc of movement of theleft-hand side U-piece is constrained by the arc-shaped track in thequadrant-shaped adjustment piece 57. The screw in the screw-and-tracklocking mechanism 58 is screwed into the constraining frame 19 and canbe tightened to clamp the position of the focus trim once it has beendetermined.

A 3D imaging device works by simulating a pair of human eyes inproviding a pair of image capturing lenses to capture a pair of imagesof the same object from different angles. The difference in the apparentposition of the object as seen from different angles is known asparallax. The human brain processes the image pair with parallax, andstereoscopic vision is the result.

When the object is relatively far away, the incident light pathsentering the pair of eyes are almost parallel, so the person looksstraight ahead. When the object is relatively close, the incident lightpaths entering the pair of eyes will have to be at an angle to thecenterline of the object with respect to the pair of eyes. Whilefocusing on a close-up object, the pair of eyes will naturally swivel sothat the optical axis of each eye converges toward the object and allowseach image to be centered on the focal plane. This is known as parallaxcompensation.

When a basic 3D imaging device is focused on a close-up object, theincident light paths entering the image-capturing lens or lenses willalso be at an angle to the centerline of he object with respect to theimaging device. When the 3D imaging device is head on to the object,both images in the pair captured will not be centered on the opticalaxis. If the device is rotated so that one image in the pair is centeredon the optical axis of the image-capturing plane on one side, then theother image will be even further de-centered from the optical axis ofthe image-capturing plane on the other side. In a real world 3D imagingdevice, the disadvantage of this is that one or both images in the pairwill be inappropriately cropped, and a lot of image information is loston one or both sides.

This invention teaches a new focusing mechanism for a 3D imaging deviceand a method for linking this focusing mechanism to another mechanismfor varying the angle of one or both optical axes in order to allow thedevice to simulate the parallax compensation function of a pair of humaneyes.

FIGS. 8A and 8B show another embodiment of the invention. The right-handside U-piece, consisting of the upper-right adjoining piece 32, shaft 33on the right-hand side, and lower-right adjoining piece 35, can have acam 59 attached to he shaft 33 to impart coordinated movement to othermechanical frameworks, such as a mirror holder 60. Adjustment of focusis tracked by means of a marked focusing scale 48 and achieved throughmovement of the right-hand side U-piece. This changes the angle of anadjustable mirror 61 which is mounted on an adjustable mirror holder 60at the same time, which changes the optical axis of the image-capturingframework on the right-hand side. The same movement of the right-handside U-piece can be linked to more than one adjustable mirror at thesame time.

FIG. 8C is a sectional view of a typical 3D imaging device with a twinlens assembly 62 and four light deflection mirrors, which define twoimage-capturing frameworks situated some distance apart, each with anoptical axis independent of the other. In FIG. 8C, one of the fourdeflection mirrors is the adjustable mirror 61 in FIGS. 8A-8B, mountedin a mirror holder 60, pivoting on a hinge joint 63. The focusing leveras embodied by the upper-right adjoining piece 32 controls the focus ofthe twin lens assembly 62 and, at the same time, imparts coordinatedmovement to the adjustable mirror 61 through the cam 59. A spring 64 iskeyed on the mirror holder 60 and reacts against the constraining frame19 to impart a force to ensure that a cam follower 65, situated at thetip of the mirror holder 60, always engages on the cam 59.

The link between the focusing lever as embodied by the upper-rightadjoining piece 32 and the adjustable mirror 61 can be calibrated suchthat the position of the image formed by the adjustable image-capturingframework on the focal plane can be used to indicate the position of thefocusing lever and, hence, determine the distance of the object from theimaging device. If the image formed by the adjustable image-capturingframework is viewed in a calibrated optical or digital viewfinder, thenthe device becomes a rangefinder. This functionality can be achievedwith or without the use of electronic components in the device.

In 3D photography, an object can be represented as an object plane whichhas width and different views when photographed from two image-capturingframeworks set apart from each other. In FIG. 8D, sectional views areshown of the 3D imaging device of FIG. 8C with light paths depicting anobject plane at infinity, mid-distance and close up. An insert of FIG.8D is also provided for clarity of illustration to show the numberedparts whose positions change in the three diagrams with light paths.

In a 3D imaging device, the image formed by the adjustableimage-capturing framework and the image formed by the otherimage-capturing framework will be viewable side-by-side in an optical ordigital viewfinder built into the image-capturing device. This pair ofimages 68, 69 is first captured on the focal plane 05. The relativeposition of this pair of images 68, 69 will indicate whether an objectplane 67 is situated at a point on the center axis of theimage-capturing device where the optical axes of the two image-capturingframeworks converge.

In FIG. 8D, when the object plane 67 is situated at this point, it willautomatically be in focus. In real life, the object plane 67 may notmove to coincide with the point where the two optical axes happen toconverge. So, in a 3D imaging device, the two optical axes are made topivot relative to each other so that the point of convergence can befound. This behavior imparts coupled focus-finding capability to thedevice. This functionality can be achieved with or without the use ofelectronic components in the device.

In practice, the 3D imaging device and adjustable mirror only needs totilt relative to the centerline and to each other by a very small amountfor parallax compensation to be effected. This almost imperceptibledisplacement is very difficult to display on an accurately scaleddrawing. The relative displacements shown in the drawings areexaggerated for clarity of illustration.

Also, in practice, the relative length of each adjoining piece formingthe U-piece may vary. All directional and positional references such asto the left, right, upper, lower, front, back, and all references torelative length and size are for the ease of understanding of thefigures. In other embodiments, the items referenced can be moved toother positions, or transformed into different shapes, or swapped withcorresponding items on the other side, and relative sizes and lengthsmay be varied as long as the basic principles described above areapplied.

The invention has been described in detail with particular emphasisbeing placed on the preferred embodiments, but variations andmodifications may occur to those skilled in the art to which theinvention pertains.

1. A focusing mount for at least one lens with an optical axis, the lensbeing fixed in a focusing tube, said focusing mount comprising: afocusing frame for fixedly holding said focusing tube, said focusingframe having at least one pair of opposing rails; and a one-piececonstraining frame operatively connected to said focusing frame; saidfocusing frame being movable relative to said constraining frame toadjust the focal point of the at least one lens, said constraining framehaving an upper face and an opposing lower face on opposite sides of thefocusing tube, and opposing side faces on opposite sides of the focusingtube; the connection between said constraining frame and said focusingframe being in the form of prismatic joints to maintain movement of saidfocusing frame relative to said constraining frame along the opticalaxis.
 2. A focusing mount according to claim 1 wherein said prismaticjoints comprise a set of rail-receiving holes for receiving therespective rails in sliding engagement.
 3. A focusing mount according toclaim 1 wherein said set of prismatic joints include a set of fourfocusing frame rails fixed to said focusing frame, and a set of fourrail-receiving holes in said constraining frame for receiving said setof four focusing frame rails.
 4. A focusing mount according to claim 1wherein said prismatic joints comprise: a pair of focusing frame railsfixed to and extending from opposite sides of said focusing frame and apair of rail-receiving holes in said constraining frame for receivingthe respective frame rails in sliding engagement, and a pair ofconstraining frame rails fixed to and extending from said constrainingframe and a pair of rail-receiving holes in said focusing frame forreceiving the respective constraining frame rails.
 5. A focusing mountaccording to claim 4 wherein said constraining frame rails comprise arigid U-piece wrapped around the remaining sides of said constrainingframe and connected to said focusing frame, and wherein said prismaticjoints comprise a pair of open slot and pin joints, said U-piece havingopposing ends; and a shaft rotatably connected to said constrainingframe and linked to said opposing ends of said U-piece.
 6. A focusingmount according to claim 1 wherein said prismatic joints comprise a pairof opposing focusing frame rails fixed to and extending from oppositesides of said focusing frame and a pair of rail-receiving holes in saidconstraining frame for receiving the respective frame rails in slidingengagement; a pair of constraining frame rails fixed to and extendingfrom said constraining frame and a pair of rail-receiving holes in saidfocusing frame for receiving the respective constraining frame rails;and wherein said focusing mount further comprises a first shaft and anopposing, parallel second shaft rotatably connected to said constrainingframe on opposite sides of said constraining frame and on opposite sidesof said focusing frame, and being perpendicular to and offset from saidpair of opposing focusing frame rails, said first and second shafts eachhaving an upper end adjacent a top face of said constraining frame and alower end adjacent a lower face of said constraining frame, wherein saidconstraining frame rails comprise a U-piece assembly wrapped around theremaining sides of said constraining frame and connected to saidfocusing frame, said U-piece assembly comprising: an upper firstadjoining piece joined to the upper end of a first of said shafts by afirst prismatic joint in the form of an upper hole and pin joint; alower first adjoining piece joined to the lower end of said first ofsaid shafts by a first prismatic joint in the form of a lower hole andpin joint; one of said upper first adjoining piece and said lower firstadjoining piece having a long arm for pivoting said upper firstadjoining piece, said first lower first adjoining piece and said firstof said shafts; an upper lever resting on the upper face of saidconstraining frame and being joined both to said upper first adjoiningpiece by a prismatic joint in the form of an upper pin and open slotjoint, and being joined to the upper end of said second shaft by asecond upper hole and pin joint; and a lower lever being disposed on thelower face of said constraining frame and being joined to said lowerfirst adjoining piece by a prismatic joint in the form of a first lowerpin and open slot joint, and being joined to the lower end of saidsecond shaft by a prismatic joint in the form of a second lower hole andpin joint.
 7. A focusing mount according to claim 6 and furthercomprising a graduated focusing scale, and wherein said long arm of oneof said upper and lower first adjoining pieces has an index mark forcooperating with said graduated scale to enable the user of saidfocusing mount to control the focus of said focusing mount.
 8. Afocusing mount according to claim 6 wherein: said upper lever comprises:an upper differential piece having a first end joined to said upperfirst adjoining piece by a prismatic joint in the form of a first upperpin and open slot joint, and an opposing second end; and an upper secondadjoining piece having a first end joined to the second opposing end ofsaid upper differential by a prismatic joint in the form of an upperhole and pin joint, and a second end joined to the upper end of saidsecond shaft by a prismatic joint in the form of a second hole and pinjoint; and said lower lever comprises: a lower differential piece havinga first end joined to said lower first adjoining piece by a prismaticjoint in the form of a first lower pin and open slot joint, and anopposing second end; and a lower second adjoining piece having a firstend joined to the second opposing end of said lower differential by aprismatic joint in the form of a lower hole and pin joint, and a secondend joined to the lower end of the second of said shafts by a prismaticjoint in the form of a second hole and pin joint.
 9. A focusing mountaccording to claim 8 wherein said upper second adjoining piececomprises: a quadrant-shaped adjustment piece having a screw andtrack-locking mechanism between said first and second ends, said screwand track mechanism having an arc-shaped track and a screw extendingthrough said track into said constraining frame for constraining thepotential arc of movement of said upper differential.
 10. A focusingmount according to claim 9 wherein said screw can be tightened to clampthe portion of the focus mount.
 11. A focusing mount for a pair ofparallel lenses fixed in a focusing tube, said focusing mountcomprising: a focusing frame for fixedly holding the focusing tube, saidfocusing frame having a pair of opposing frame rails; an integralconstraining frame operatively connected to said focusing frame formounting said focusing frame to adjust the focal points of therespective parallel lens, said constraining frame having an upper faceand an opposing, parallel lower face on opposite sides of said focusingframe, said opposing frame rails of said focusing frame being connectedto said upper and lower faces of said constraining frame by hole and pinjoints to enable movement of said focusing frame to extend along theoptical axes of said pair of lenses, said constraining frame comprisingconstraining frame rails; and a first shaft and an opposing, parallelsecond shaft rotatably connected to said constraining frame on oppositesides of said focusing frame extending between said upper face and saidlower face of said constraining frame, said first and second shafts eachhaving an upper end adjacent said upper face of said constraining frameand a lower end adjacent said lower face of said constraining frame;said constraining frame rails comprising: a U-piece assembly wrappedaround the remaining sides of said constraining frame and connected tosaid focusing frame, said U-piece assembly comprising: an upper firstadjoining piece joined to the upper end of said first shaft by a firstupper hole and pin joint; a lower first adjoining piece joined to thelower end of said first shaft by a first lower hole and pin joint; oneof said upper first adjoining piece and said lower first adjoining piecehaving a long arm for pivoting said upper first adjoining piece, saidlower first adjoining piece and said first shaft; an upper differentialpiece having a first end joined to said upper first adjoining piece by afirst upper pin and open slot joint, and an opposing second end; anupper second adjoining piece comprising a first end connected to thesecond end of said differential piece by a pin and hole joint and asecond end joined to the upper end of said second shaft by a pin andhole joint, a quadrant-shaped adjustment piece having a screw andtrack-locking mechanism between said first and second ends, said screwand track mechanism having an arc shaped track and a screw extendingthrough said track into said constraining frame; a cam attached to thefirst of said shafts; and at least one mirror holder holding anadjustable mirror for changing the optical axis of an image capturingframework, said mirror holder being pivotally mounted to a pivot shaftand in operative engagement with said cam for adjusting images inresponse to movement by said long arm.
 12. A 3-D focusing system for a3-D camera, said 3-D focusing system comprising: a focusing frame; atwin lens assembly including a pair of lenses mounted in said focusingframe, said pair of lenses having a pair of parallel optical axes; afirst pair of mirrors, each located on a different one of the paralleloptical axes of said pair of lenses, said first pair of mirrors beingfixed, each of said first pair of mirrors being tilted to reflect lightin a generally opposite direction across the optical axis of the otherof said lenses; a second pair of mirrors, each of said second pair ofmirrors being in the path of reflection of a different one of said firstpair of mirrors and located on the opposite side of said optical axesfrom the mirror of said first pair of mirrors from which said respectivemirror of said second pair of mirrors receives reflective light, saidsecond pair of mirrors being tilted to reflect light in the generaldirection of an object plane, at least one of said second pair ofmirrors being adjustable to change the tilt of said at least one of saidsecond pair of mirrors to change the angle of reflection of lightimpinging on said at least one adjustable mirror; an adjusting structureoperably connected to both said adjusting frame and said at least oneadjustable mirror, said adjusting structure simultaneously moving saidfocusing frame along said parallel optical axes and said at least oneadjustable mirror, and adjusting the tilt of said at least oneadjustable mirror to vary the direction of one or both of the opticalaxes of the light being reflected from the lens transmitting light tothe respective at least one of said adjustable mirrors to capture a pairof images focused on an object plane from different angles to performparallax compensation to eliminate double vision.
 13. A 3-D focusingsystem according to claim 12 wherein said second pair of mirrorscomprises a fixed mirror tilted to reflect light from the lenstransmitting light to said fixed mirror of said second pair of mirrorstowards the optical axes of said pair of lenses, and an adjustablemirror, said adjustable mirror being adjustable to change the tilt ofsaid adjustable mirror to change the angle of reflection of lightimpinging on said adjustable mirror; wherein said adjusting structure isoperably connected to both said adjusting frame and to said adjustablemirror.
 14. A 3-D focusing system according to claim 12 and furthercomprising: a constraining frame for holding said twin lens assembly,said first pair of mirrors, said second pair of mirrors and saidadjusting structure, said constraining frame having opposing first andsecond sides on opposite sides of parallel optical axes and beingparallel to said parallel optical axes, and opposing second and thirdsides on opposite sides of said parallel optical axes, said second andthird sides being transverse to said first and second sides; said twinlens assembly, said at least one adjustable mirror and said adjustingstructure being movably mounted on said constraining frame; and anadjustable mirror holder for holding each of said at least oneadjustable mirror; wherein said adjusting structure comprises: a firstadjoining piece proximate said first side of said constraining frame; asecond adjoining piece proximate said second side of said constrainingframe and opposite said first adjoining piece; a first shaft joiningsaid first and second adjoining pieces and rotatably mounted on saidconstraining frame; adjustment structure interconnecting said firstshaft and said adjustable mirror holder; a first differential pieceproximate said first side of said constraining frame and being pivotablyconnected to said first adjoining piece; a second differential pieceproximate said second side of said constraining frame and beingpivotally connected to said second adjoining piece; a first adjustmentpiece proximate said first side of said constraining frame and beingpivotably connected to said first differential piece; a secondadjustment piece proximate said second side of said constraining frameand being pivotably connected to said second differential piece; asecond shaft parallel to said first shaft and joining said firstadjustment piece and said second adjustment piece; and a focusing railfixed to said focusing frame and being slidably mounted on saidconstraining frame for sliding movement parallel to said optical axesfor changing the object plane of said pair of lenses; said focusingframe being pivotably connected to said first differential piece andsaid second differential piece; said focusing frame effecting themovement of said first and second differential pieces to rotate saidfirst and second shafts to move said adjusting structure and to movesaid mirror holder to move said at least one adjustable mirror tocapture a pair of images focused on an object plane from differentangles to perform parallax compensation to eliminate double vision.